How can I create a shortcut to Shadeless?
I have made an addon for you because I already created it to enable similar custom shortcuts (Show Only Render and Show Edges).


Copy the addon file
https://raw.githubusercontent.com/jendabek/blender_misc/master/custom_shortcuts_enable.py
to Blender\2.X\scripts\addons
Enable it in User Preferences CtrlAltU > Addons, it is called Custom Shortcuts Enable.
Create a new shortcut in the User Preferences > Input > Screen section and insert the screen.trigger_shadeless as the operator name:



Set some key combination.


That shortcut should trigger shadeless on / off on the selected material.